1. Field of the Invention
The invention relates to apparatus for connecting an electrical device to a power source and, more particularly, universally adapting a single-voltage device to different source voltages.
2. Description of the Prior Art
Electrical devices, such as copiers, computers, audio components, household appliances, etc., frequently operate on only one voltage but must be used with different power supply voltages. For example, a 115 VAC 60 Hz copier wired with a 115 VAC 60 Hz style plug may have to be used where only a 230 VAC 60 Hz power supply outlet is available. Substitution of a 230 VAC 60 Hz plug together with appropriate wire reconnections permit 115 VAC copier operation from the 230 VAC outlet. However, serious hazards to an operator and machine safety are created. For example, a plug or socket wiring error introduces 230 VAC to copier parts designed for 110 VAC. The reverse situation creates analogous problems. In addition to the hazards of rewiring a 230 VAC device for 110 VAC outlets, the lower supply voltage will probably not effectively operate most 230 VAC devices.
Electrical devices incorporate solutions to some of these problems. The 115 VAC IBM Series III copier connects directly to 230 VAC power supply voltage through appropriate wiring between its internal components and a 230 VAC plug. A line cord adapter, when placed between the 230 VAC plug and a 115 VAC power supply socket, provides essential wiring interconnections, but does not affect the copier's voltage requirements. Voltage switches advertised in ELECTRONIC DESIGN, Nov. 22, 1980, page 296, permit different power supply voltage connections, but do not insure that the switch positions match the connected voltages. IBM TECHNICAL DISCLOSURE BULLETIN, December 1976, pages 2444 and 2445 describe a special circuit for protecting a copier/collator from being inadvertently plugged into the wrong line. Keyed mating plugs and sockets appear in IBM TECHNICAL DISCLOSURE BULLETIN, July 1972, pages 624 and 625, and German Publication No. 2,243,825, Mar. 14, 1974. Alternatively, separate device-mounted sockets for each possible power supply voltage and matching, removable line-cord sets for each power source voltage may be provided with the device. The latter solution requires circuits for removing electrical potential from unused sockets. French Pat. No. 1,545,854 discloses two sockets, one covered, alternately selectable, connected to a power supply voltage changing switch. U.S. Pat. Nos. 2,930,019 and 2,989,719 disclose plugs and sockets adjustable for a plurality of power sources. However, since each must be manually rewired for different voltage sources, a voltage mismatch is possible. Portable radios provide one receptacle both for 110 VAC operation and, specially slotted, for 12 VDC automobile operation. A 12 VDC socket projection switches the power source directly into the radio's DC power supply. In French Pat. No. 1,503,482, a notched dial rests on a plug inserted into an electric razor. While the dial operates a circuit adapting the razor's voltage, operator error connects the wrong power supply voltage.
The prior art does not teach a single device receptacle uniquely mated to each one of a multiplicity of line-cord sets and to the device's power supply, wherein inadvertent mismatches cannot occur.
The invention provides plural plug and socket line-cord sets, usable with a device having a variable power interface, for assuring that the plug's supply voltage matches the device's input voltage. Each line-cord set has two essentially permanently attached end connectors: a keyed socket and a wall plug. The keyed socket has a unique predetermined configuration for the one supply voltage to which the wall plug at the other end is designed to connect. A device receptacle connected to the device's power interface receives the line-cord's keyed socket. An adjustable key on the device mates with the keyed socket's configuration and rejects nonmating line-cord sockets. Adjusting the receptacle's key to mate with the keyed socket plug; (a) admits the line-cord socket into the receptacle and (b) varies the device's power interface to match the device's input voltage to the supply voltage for which the wall plug is designed.